Optical film

ABSTRACT

An optical film comprising a copolycarbonate composed of 25 to 90 mol % of unit (A) of the following formula, 
                         
and 10 to 75 mol % of unit (B) of the following formula,
 
                         
wherein the substituents are defined herein, and the optical film satisfies the following expression (1), R(450)&lt;R(550)&lt;R(650) (1), wherein R(450), R(550) and R(650) are in-plane retardation values of the film at wavelengths of 450 nm, 550 nm and 650 nm. The optical film exhibits a desired chromatic dispersion, low photoelasticity and excellent melt processability.

This Application is a Continuation-in-part Application of InternationalApplication No. PCT/JP2009/070446 filed Dec. 1, 2009.

TECHNICAL FIELD

This invention relates to an optical film. More specifically, it relatesto an optical film having a desired chromatic dispersion, having a lowphotoelastic constant and high heat resistance and having excellent meltprocessability.

BACKGROUND ART

An optical film is used as a retardation film or a protective film for apolarizing plate. The retardation film is used in a liquid crystaldisplay, and has functions of color compensation, broadening of aviewing angle and prevention of reflection. As a retardation film, a λ/4film and a λ/2 film are known, and a polycarbonate, a polyether sulfoneand a polysulfone are used as materials therefor. λ/4 films and λ/2films formed from these materials have the property of having a largerphase difference as the wavelength gets shorter. There is hence involveda problem that the wavelength capable of functioning as a λ/4 film and aλ/2 film is limited to specific wavelengths.

As a method of controlling a wavelength in a broad band, there is knowna method of stacking two or more birefringence films having differentdependency of phase difference on wavelength at specific angles (PatentDocument 1). This method requires the steps of attaching a plurality ofretardation films and adjusting attaching angles and hence has a problemon productivity. Further, since the thickness of the entire retardationfilms is increased, there is involved a problem that the lighttransmittance is decreased to get dark.

In recent years, there is proposed a method of controlling a wavelengthin a broad band by means of one film without stacking (Patent Document2). That is a method using a copolycarbonate composed of a unit havingpositive refractivity anisotropy and a unit having negative refractivityanisotropy. However, this copolycarbonate has a high melting temperaturesince it contains a unit derived from fluorene-based bisphenol, andthere is involved a problem that a gel substance formed by decompositionis liable to be generated when it melted. Further, it has a high glasstransition temperature (Tg) and requires a high temperature for filmstretching, and it requires an unconventional special processingapparatus. Further, it has a high photoelastic constant and has a largebirefringence due to a stress, and it has a problem that a lightomission takes place when it is used as a retardation film.

On the other hand, there is already proposed a low-photoelastic-constantcopolycarbonate formed from an aliphatic diol to be used for an opticaldisc (Patent Document 3). In this document, however, nothing has beenstudied with regard to the stretchability of the film and the chromaticdispersion. Further, the photoelastic constant of the copolycarbonatedescribed in this document is required to be further decreased when itis used as a retardation film or a protective film for a polarizingplate.

Further, there is reported a low-photoelastic-constant retardation filmformed from a copolycarbonate containing a fluorene component and anisosorbide component (Patent Document 4). Since this copolycarbonate isa termpolymer, it is required to precisely control the compositionalratio of three components for controlling the chromatic dispersion, andits stable production is not easy. Further, since it has low thermalstability, it has a defect that its molecular weight is liable to bedecreased during melt-processing.

There is also proposed a retardation film formed from a copolycarbonatecontaining a fluorene-based bisphenol structure (Patent Documents 5 and6). Further, there is also proposed a polarizing plate protective filmformed from a copolycarbonate containing a fluorene-based bisphenolstructure (Patent Document 7). However, any one of these has a highglass transition temperature (Tg), and a high temperature is requiredfor stretching a film, so that an unconventional special processingapparatus is required. Further, they have high photoelastic constantsand large birefringence due to a stress, and they have a problem that alight omission takes place when they are used as retardation films.

-   (Patent Document 1) JP-A 2-120804-   (Patent Document 2) Japanese Patent No. 3325560-   (Patent Document 3) JP-A 2004-67990-   (Patent Document 4) International Publication No. 06/041190-   (Patent Document 5) International Publication No. 01/009649-   (Patent Document 6) JP-A 2006-323254-   (Patent Document 7) Japanese Patent No. 3995387

DISCLOSURE OF THE INVENTION

It is an object of this invention to provide an optical film formed of acopolycarbonate having a desired chromatic dispersion and having lowphotoelasticity and excellent melt processability.

The present inventor has made diligent studies and found that an opticalfilm comprising a copolycarbonate of a diol having a fluorene structurein a side chain with a specific aliphatic diol exhibits an inversechromatic dispersion of a phase difference being smaller with a decreasein wavelength and has a low photoelastic constant and excellent meltprocessability, and this invention has been accordingly arrived at.

That is, this invention is an optical film comprising a copolycarbonatecomposed of 25 to 90 mol % of unit (A) of the following formula,

wherein each of R₁ and R₂ is independently a hydrogen atom, ahydrocarbon group having 1 to 10 carbon atoms or a halogen atom, each ofR₃ and R₄ is independently a hydrocarbon group having 1 to 10 carbonatoms, each of m and n is independently an integer of 0 to 4, and eachof p and q is independently an integer of 0 or more,

and 10 to 75 mol % of unit (B) of the following formula

wherein R^(a) is a monocyclic or polycyclic alicyclic hydrocarbon grouphaving 4 to 20 carbon atoms, the alicyclic hydrocarbon group may containa hetero atom or may have a bridge structure, and q is 0 or 1,

the optical film satisfying the following expression (1),R(450)<R(550)<R(650)  (1)

wherein R(450), R(550) and R(650) are in-plane retardation values of thefilm at wavelengths of 450 nm, 550 nm and 650 nm, respectively.

The optical film of this invention can be used as a retardation film.This invention also includes a liquid crystal display provided with theabove retardation film.

PREFERRED EMBODIMENTS OF THE INVENTION

This invention will be explained in detail below. The optical film ofthis invention comprises a copolycarbonate composed of unit (A) and unit(B).

(Unit (A))

The unit (A) is represented by the following formula.

In the unit (A), each of R₁ and R₂ is independently a hydrogen atom, ahydrocarbon group having 1 to 10 carbon atoms or a halogen atom. Thehydrocarbon group includes an alkyl group having 1 to 10 carbon atoms, acycloalkyl group having 5 to 10 carbon atoms, an aryl group having 6 to10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms and analkenyl group having 1 to 10 carbon atoms. The alkyl group having 1 to10 carbon atoms includes methyl, ethyl, butyl, etc. The halogen atomincludes a fluorine atom, a chlorine atom, a bromine atom, etc.

Each of R₃ and R₄ is independently a hydrocarbon group having 1 to 10carbon atoms. The hydrocarbon group is preferably an alkylene grouphaving 1 to 10 carbon atoms, more preferably an alkylene group having 1to 4 carbon atoms, still more preferably an ethylene group.

p and q are repetition numbers of —(R₃—O)— and —(O—R₄)—. Each of p and qis independently an integer of 0 or more, preferably an integer of 0 to20, more preferably an integer of 0 to 12, still more preferably aninteger of 0 to 8, particularly preferably an integer of 0 to 4, mostpreferably an integer of 0 or 1. Each of m and n is independently aninteger of 0 to 4.

(Unit (A1))

The unit (A) is preferably a unit (A1) of the following formula in whichp and q are 0.

wherein R₁, R₂, m and n are as defined in the unit (A).

The unit (A1) includes units derived from9,9-bis(4-hydroxyphenyl)fluorene,9,9-bis(4-hydroxy-3-methylphenyl)fluorene,9,9-bis(4-hydroxy-3-ethylphenyl)fluorene,9,9-bis(4-hydroxy-3-n-propylphenyl)fluorene,9,9-bis(4-hydroxy-3-n-isopylphenyl)fluorene,9,9-bis(4-hydroxy-3-n-butylphenyl)fluorene,9,9-bis(4-hydroxy-3-sec-butylphenyl)fluorene,9,9-bis(4-hydroxy-3-tert-butylphenyl)fluorene,9,9-bis(4-hydroxy-3-cyclohexylphenyl)fluorene, and9,9-bis(4-hydroxy-3-phenylphenyl)fluorene. These compounds forintroducing the units (A1) may be used singly or in combination of twoor more of them.

(Unit (A2))

The unit (A) is preferably a unit (A2) of the following formula, derivedfrom 9,9-bis(4-hydroxy-3-methylphenyl)fluorene.

In the copolycarbonate comprising unit (A2), the b value when a solutionof 10 g thereof in 50 ml of ethanol is measured in an optical distanceof 30 mm is preferably 6.0 or less, more preferably 5.5 or less, stillmore preferably 5.0 or less. When the b value is in the above range, anoptical film formed from the copolycarbonate has a good hue and has highstrength.

The 9,9-bis(4-hydroxy-3-methylphenyl)fluorene as a raw material for theunit (A2) can be obtained by a reaction between o-cresol and fluorenone.The 9,9-bis(4-hydroxy-3-methylphenyl)fluorene having a small b value canbe obtained by removing impurities.

Specifically, purified 9,9-bis(4-hydroxy-3-methylphenyl)fluorene can beobtained by distilling off unreacted o-cresol after the reaction betweeno-cresol and fluorenone, dissolving the residue in an alcohol, ketone orbenzene derivative solvent, adding activated clay or activated carbonthereto, filtering the solution, and then, filtering a crystallizedproduct from a filtrate. The impurities that are to be removed are a2,4′-dihydroxy material, a 2,2′-dihdyroxy material and impurities havingunknown structures. The alcohol solvent that is used for the abovepurification preferably includes lower alcohols such as methanol,ethanol, propanol and butanol. The ketone solvent preferably includeslower aliphatic ketones such as acetone, methyl ethyl ketone, methylisopropyl ketone and cyclohexanone and mixtures of these. The benzenederivative solvent preferably includes toluene, xylene, benzene andmixtures of these. The amount of the solvent is sufficiently an amountin which the fluorene compound is fully dissolved, and it is generallyapproximately twice to 10 times the amount of the fluorene compound. Theactivated clay can be selected from commercially available activatedclay formed of a powdery or particulate silica-alumina. Further, theactivated carbon can be selected from commercially available activatedcarbon in the form of a power or particles.

(Unit (A3))

The unit (A) is preferably a unit (A3) of the following formula in whichp and q are integers of 1 or more.

wherein R₁, R₂, m, n, R₃ and R₄ are as defined in the unit (A). Each ofp and q is independently preferably an integer of 1 to 20, morepreferably an integer of 1 to 12, still more preferably an integer of 1to 8, particularly preferably an integer of 1 to 4, most preferably 1.

The unit (A3) includes units derived from9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene,9,9-bis[4-(3-hydroxypropoxy)phenyl]fluorene,9,9-bis[4-(4-hydroxybutoxy)phenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-methylphenyl]fluorene,9,9-bis[2-(2-hydroxyethoxy)-5-methylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-ethylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-propylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-isopropylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-n-butylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-isobutylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-(1-methylpropyl)phenyl]fluorene,9,9-bis[4-(3-hydroxypropoxy)-3-methylphenyl]fluorene,9,9-bis[4-(4-hydroxybutoxy)-3-methylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-dimethylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-2,5-dimethylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-diethylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-dipropylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-diisopropylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-di-n-butylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-diisobutylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-bis(1-methylpropyl)phenyl]fluorene,9,9-bis[4-(3-hydroxypropoxy)-3,5-dimethylphenyl]fluorene,9,9-bis[4-(4-hydroxybutoxy)-3,5-dimethylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-cyclohexylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-diphenylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-benzylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-dibenzylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-propenylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-fluorophenyl]fluorene, and9,9-bis(hydroxyalkoxyphenyl)fluorenes of these. Further, it includesunits derived from 9,9-bis[hydroxypoly(alkyleneoxy)phenyl]fluorenes ofthe above formula in which p and q are 2 or more.

Of these, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene and9,9-bis[4-(2-hydroxyethoxy)-3-methylphenyl]fluorene are preferred.

The above compounds for introducing the unit (A3) may be used singly orin combination of two or more of them.

Compounds for introducing the unit (A3) can be obtained by reacting9,9-bis(hydroxyphenyl)fluorenes with compounds (alkylene oxide,haloalkanol, etc.) corresponding to the groups R₃ and R₄. For example,9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene can be obtained by addingethylene oxide to 9,9-bis(4-hydroxyphenyl)fluorene, and9,9-bis[4-(3-hydroxypropoxy)phenyl]fluorene can be obtained, forexample, by reacting 9,9-bis[4-hydroxyphenyl]fluorene with3-chloropropanol under an alkaline condition. In addition,9,9-bis(hydroxyphenyl)fluorene can be obtained by a reaction between afluorenone (9-fluorenone, etc.) and a corresponding phenol, and9,9-bis(4-hydroxyphenyl)fluorene can be obtained, for example, by areaction between a phenol and 9-fluorenone.

(Unit (A4))

As the unit (A3), a unit (A4) of the following formula, derived from9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (BPEF), is preferred.

A copolycarbonate comprising the units (A1) and (A2) has excellent heatresistance and a low photoelastic constant as compared with acopolycarbonate comprising the units (A3) and (A4), so thatnon-uniformity is not thermally easily caused.

(Unit (B))

The unit (B) is represented by the following formula.

In the formula, R^(a) is a monocyclic or polycyclic alicyclichydrocarbon group having 4 to 20 carbon atoms, the above alicyclichydrocarbon group may contain a hetero atom and also may have a bridgestructure, and q is 0 or 1.

R^(a) includes a cycloalkylene group which may have a substituent. Thecycloalkylene group includes a cyclobutylene group, a cyclohexylenegroup of the following formula, a cyclooctylene group and acyclodecylene group.

wherein R⁷ is an alkyl group having 1 to 12 carbon atoms or a hydrogenatom.

R^(a) includes a group of the following formula.

R^(a) includes a group of the following formula. Specifically, itincludes a tricyclodecane-diyl group and a pentacyclodecane-dinyl group.

wherein r is 0 or 1.

R^(a) includes a group of the following formula, such as a decaline-diylgroup.

wherein s is 0 or 1.

R^(a) includes a norbornene-diyl group having a bridge structure,represented by the following formula.

R^(a) includes an adamantane-diyl group having a bridge structure,represented by the following formula.

R^(a) includes a group having a hetero atom, represented by thefollowing formula.

The hetero atom includes oxygen, nitrogen, phosphorus and sulfur atoms.The heteroatom preferably includes oxygen, nitrogen and sulfur atoms,and it is more preferably an oxygen atom.

R^(a) in the unit (B) is preferably at least one group selected from theclass consisting of an optionally substituted cycloalkylene group having4 to 20 carbon atoms, an optionally substituted cycloalkoxylene grouphaving 4 to 20 carbon atoms,

in which each of r and s is independently 0 or 1.

The optionally substituted cycloalkylene group having 4 to 20 carbonatoms includes a cyclobutylene group, a cyclohexylene group and acyclooctylene group. The substituent includes an alkyl group having 1 to3 carbon atoms such as methyl, ethyl and propyl, and halogen atoms suchas a fluorine atom, a chlorine atom and a bromine atom.

The optionally substituted cycloalkoxylene group having 4 to 20 carbonatoms includes a cyclobutoxylene group, a cyclohexyloxylene group and acyclooctyloxylene group. The substituent includes an alkyl group having1 to 3 carbon atoms such as methyl, ethyl and propyl, and halogen atomssuch as a fluorine atom, a chlorine atom and a bromine atom.

The unit (B) includes a unit (Ba) of the following formula in which q is1 and a unit (Bb) of the following formula in which q is 0.

in which R^(a) is as defined in the unit (B).

in which R^(a) is as defined in the unit (B).

(Unit (B1))

The unit (B) is preferably a unit (B1) of the following formula.

The unit (B1) is a unit derived from an ether diol, and the above etherdiol specifically includes a unit (B1-1) derived from isosorbide, a unit(B1-2) derived from isomannide and a unit (B1-3) derived from isoididewhich have the relationships of being stereoisomers to one another.

These ether diols derived from sugar are substances that are alsoobtained from biomass in nature and are ones of so-called renewableresources. Isosorbide can be obtained by hydrogenating D-glucoseobtained from starch and then subjecting it to dehydration. The otherether diols can be also obtained by like reactions except for startingmaterials.

In particular, the unit is preferably a unit derived from isosorbide(1,4,3,6-dianhydro-D-sorbitol). Isosorbide is an ether diol that can beeasily prepared from starch, etc., and is available in abundance as amaterial, and it is excellent in all of easiness in production,properties and broadness in use as compared with isomannide andisoidide.

(Unit (B2))

The unit (B) is preferably a unit (B2) of the following formula.

(Unit (B3))

The unit (B) is preferably a unit (B3) of the following formula.

(Unit (B4))

The unit (B) is preferably a unit (B4) of the following formula.

Therefore, the copolycarbonate preferably comprises unit (A2) of thefollowing formula,

and at least one unit (Bi) selected from the class consisting units ofthe following formulae.

Further, the copolycarbonate preferably comprises a unit (A4) of thefollowing formula,

and at least one unit (Bi) selected from the class consisting of unitsof the following formulae.

(Compositional Ratio)

In the copolycarbonate, the content of the unit (A) is 25 to 90 mol %,preferably 30 to 90 mol %, and the content of the unit (B) is 10 to 75mol %, preferably 10 to 70 mol %.

When the content of the unit (A) is less than 25 mol %, the chromaticdispersion of the copolycarbonate is no longer any inverse dispersionproperty, and there is caused a problem on the optical properties. Whenthe content of the unit (A) exceeds 90 mol %, the glass transitiontemperature of the copolycarbonate is high, and there is caused aproblem on the processability. Further, the photoelastic constant isover 30×10⁻¹² Pa⁻¹. The compositional ratio is required to be controlledsuch that the compositional ratio after the polymerization has adeviation of 0.5 mol % or less, preferably 0.3 mol % or less, from thecompositional ratio on the charged amount basis. When it exceeds 0.5 mol%, the chromatic dispersion changes to a great extent, and it leads to aquality problem. The contents of the unit (A) and the unit (B) aremeasured and calculated on the basis of the proton NMR of JNM-AL400supplied by JEOL Ltd.

The contents of the unit (A) and the unit (B) can be adjusted byblending a polycarbonate formed of unit (A) alone or a polycarbonateformed of unit (B) alone with a copolycarbonate comprising the unit (A)and the unit (B).

(Glass Transition Temperature: Tg)

The glass transition temperature (Tg) of the copolycarbonate ispreferably 100 to 200° C., more preferably 140 to 200° C., still morepreferably 140 to 180° C. When the glass transition temperature (Tg) islower than 100° C., heat resistance stability is poor, and a retardationvalue changes with time, which may sometimes affect the display quality.When the glass transition temperature (Tg) is higher than 200° C.,melt-polymerization is difficult since the viscosity is too high. Theglass transition temperature (Tg) is measured with 2910 type DSCsupplied by T. A. Instruments (Japan) at a temperature elevation rate of20° C./minute.

(Photoelastic Constant)

The absolute value of photoelastic constant of the copolycarbonate ispreferably 30×10⁻¹² Pa⁻¹ or less, more preferably 28×10⁻¹² Pa⁻¹ or less,still more preferably 25×10⁻¹² Pa⁻¹ or less. When the absolute value islarger than 30×10⁻¹² Pa⁻¹, undesirably, birefringence caused by a stressis large, and a light omission takes place when it is used as aretardation film. The photoelastic constant is measured by taking a 50mm long and 10 mm wide test piece from a film and measuring it with aspectroellipsometer M-220 supplied by JASCO Corporation.

(Production of Copolycarbonate)

The copolycarbonate can be produced by melt-polymerizing afluorenedihydroxy component, an aliphatic diol component and a carbonatediester.

The fluorenedihydroxy component is represented by the following formula.

wherein R₁, R₂, R₃, R₄, m, n, p and q are as defined in the unit (A).

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes 1,2-cyclohexanedimethanol,1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol.

wherein R₇ is an alkyl group having 1 to 12 carbon atoms or a hydrogenatom.

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes tricyclodecanedimethanol andpentacyclodecanedimethanol.

wherein r is 0 or 1.

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes 2,6-decalindimethanol,1,5-decalindimethanol and 2,3-decalindimethanol.

wherein s is 0 or 1.

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes 2,3-norbornanedimethanol and2,5-norbornanedimethanol.

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes 1,3-adamantanedimethanol.

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes 1,2-cyclohexanediol,1,3-cyclohexanediol and 1,4-cyclohexanediol.

wherein R₈ is an alkyl group having 1 to 12 carbon atoms or a hydrogenatom.

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes tricyclodecanediol andpentacyclodecanediol.

wherein r is 0 or 1.

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes 2,6-decalindiol, 1,5-decalindiol and2,3-decalindiol.

wherein s is 0 or 1.

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes 2,3-norbornanediol and2,5-norbornanediol.

The aliphatic diol component includes compounds of the followingformula. Specifically, it includes 1,3-adamantanediol.

The aliphatic diol component includes hetero-atom-possessing compoundsof the following formulae.

The carbonate diester includes esters of an optionally substituted arylgroup having 6 to 12 carbon atoms or an aralkyl group. Specifically, itincludes diphenyl carbonate, ditolyl carbonate,bis(chlorophenyl)carbonate and bis(m-cresyl)carbonate. Of these,diphenyl carbonate is particularly preferred.

The amount of the diphenyl carbonate for use per mole of total ofdihydroxy compounds is preferably 0.97 to 1.10 mol, more preferably 1.00to 1.06 mol.

For accelerating the polymerization speed in the melt-polymerizationmethod, a polymerization catalyst may be used. The polymerizationcatalyst includes an alkali metal compound, an alkaline earth metalcompound, a nitrogen-containing compound and a metal compound.

Organic acid salts, inorganic acid salts, hydroxides, hydrides,alkoxides and quaternary ammonium hydroxides of alkali metals andalkaline earth metals are preferably used as such compounds. Thesecompounds may be used singly or in combination.

The alkali metal compound includes sodium hydroxide, potassiumhydroxide, cesium hydroxide, lithium hydroxide, sodium bicarbonate,sodium carbonate, potassium carbonate, cesium carbonate, lithiumcarbonate, sodium acetate, potassium acetate, cesium acetate, lithiumacetate, sodium stearate, potassium stearate, cesium stearate, lithiumstearate, sodium borohydride, sodium benzoate, potassium benzoate,cesium benzoate, lithium benzoate, disodium hydrogen phosphate,dipotassium hydrogen phosphate, dilithium hydrogen phosphate anddisodium phenylphosphate. It also includes disodium salt, dipotassiumsalt, dicesium salt and dilithium salt of bisphenol A, and also includessodium salt, potassium salt, cesium salt and lithium salt of phenol.

The alkaline earth metal compound includes magnesium hydroxide, calciumhydroxide, strontium hydroxide, barium hydroxide, magnesium carbonate,calcium carbonate, strontium carbonate, barium carbonate, magnesiumdiacetate, calcium diacetate, strontium diacetate and barium diacetate.

The nitrogen-containing compound includes quaternary ammonium hydroxideshaving an alkyl or aryl group, such as tetramethylammonium hydroxide,tetraethylammonium hydroxide, tetrapropylammonium hydroxide,tetrabutylammonium hydroxide and trimethylbenzylammonium hydroxide. Italso includes tertiary amines such as triethylamine, dimethylbenzylamineand triphenylamine, and imidazoles such as 2-methylimidazole,2-phenylimidazole and benzoimidazole. Further, it also includes bases orbasic salts such as ammonia, tetramethylammonium borohydride,tetrabutylammonium borohydride, tetrabutylammonium tetraphenylborate andtetraphenylammonium tetraphenylborate. The metal compound includes azinc aluminum compound, a germanium compound, an organotin compound, anantimony compound, a manganese compound, a titanium compound and azirconium compound. These compounds may be used singly or in combinationof two or more of them.

The amount of the polymerization catalyst for use per mole of the diolcomponent is preferably 1×10⁻⁹ to 1×10⁻² equivalent weight, morepreferably 1×10⁻⁸ to 1×10⁻³ equivalent weight, still more preferably1×10⁻⁷ to 1×10⁻³ equivalent weight.

The melt polycondensative reaction is carried out by heating a reactionsystem in an inert gas atmosphere under reduced pressure with stirringand thereby distilling off a formed monohydroxy compound as isconventionally known.

The reaction temperature is normally in the range of 120 to 350° C., andat a later stage of the reaction, the degree of reduced pressure isincreased to 10 to 0.1 Torr to easily distill off the formed monohydroxycompound, whereby the reaction is completed. A terminal stopper and anantioxidant may be added as required.

At a later stage of the reaction, a catalyst deactivator may be added.Known catalyst deactivators can be effectively used as a catalystdeactivator, and ammonium salt or phosphonium salt of sulfonic acid isabove all preferred. Further, salts of dodecylbenzenesulfonic acid suchas dodecylbenzenesulfonic acid tetrabutylphosphonium salt and salts ofp-toluenesulfonic acid such as p-toluenesulfonic acid tetrabutylammoniumsalt are preferred.

Further, the catalyst deactivator is preferably selected from esters ofsulfonic acids such as methyl benzenesulfonate, ethyl benzenesulfonate,butyl benzenesulfonate, octyl benzenesulfonate, phenyl benzenesulfonate,methyl p-toluenesulfonate, ethyl p-toluenesulfonate, butylp-toluenesulfonate, octyl p-toluenesulfonate and a phenylp-toluenesulfonate. Of these, dodecylbenzenesulfonic acidtetrabutylphosphonium salt is most preferably used. When at least onepolymerization catalyst selected from alkali metal compounds and/oralkaline earth metal compounds is used, the amount of the catalystdeactivator that can be used per mole of the catalyst is 0.5 to 50 mol,more preferably 0.5 to 10 mol, still more preferably 0.8 to 5 mol.

Further, additives such as a thermal stabilizer, a plasticizer, aphotostabilizer, a polymerization metal deactivating agent, a flameretardant, a lubricant, an antistatic agent, a surfactant, ananti-fungus agent, an ultraviolet absorbent and a mold release agent maybe added as required depending upon fields of use.

(Production of Optical Film)

The optical film can be produced, for example, by a solution castingmethod, a melt-extrusion method, a hot pressing method or a calendermethod. Of these, a melt-extrusion method is preferred from theviewpoint of productivity.

In the melt-extrusion method, a method of extruding a resin through aT-die and sending an extrudate to a cooling roll is preferably used. Thetemperature at this time is determined depending upon the molecularweight, Tg and melt-flowability of the copolycarbonate, while it is inthe range of 180 to 350° C., more preferably in the range of 200° C. to320° C. When it is lower than 180° C., undesirably, the viscosity ishigh, the orientation and stress strain of the polymer are liable toremain. When it is higher than 350° C., the problems of thermaldeterioration, coloring and die lines (streaks) from T-die are liable tobe caused.

Further, since the copolycarbonate used in this invention has goodsolubility in an organic solvent, a solution casting method can be alsoapplied. In the solution casting method, the solvent can be suitablyselected from methylene chloride, 1,2-dichloroethane,1,1,2,2-tetrachloroethane, dioxolane or dioxane. The content of aresidual solvent in the film in the solution casting method ispreferably 2% by weight or less, more preferably 1% by weight or less.When it exceeds 2% by weight, the residual solvent is too much, and theglass transition temperature of the film is greatly decreased, which isundesirable in respect of heat resistance.

The thickness of an unstretched film is preferably in the range of 30 to400 μm, more preferably in the range of 40 to 300 μm. When the abovefilm is further stretched to form a retardation film, it can bedetermined as required in the above range while a desired retardationvalue and thickness of the optical film are taken into account.

The thus-obtained unstretched film is stretched to give a retardationfilm. As a stretching method, there may be employed a known method ofmonoaxial stretching in the machine direction, monoaxial stretching inthe transverse direction with a stenter, concurrent biaxial stretchingthat is a combination of these, or consecutive biaxial stretching.Further, a continuous method is preferred in view of productivity, whilea batch method may be employed. The stretching temperature is preferablyin the range of (Tg−20° C.) to (Tg+50° C.), more preferably in the rangeof (Tg−10° C.) to (Tg+30° C.), in which Tg is a glass transitiontemperature of the copolycarbonate. In the above temperature range,preferably, the molecular motion of the polymer is proper, therelaxation by stretching takes place with difficulty, the inhibition oforientation is easy and an in-plane phase difference is easily obtained.

The stretch ratio is determined depending upon an intended retardationvalue, while the stretch ratio in each of the machine and transversedirections is 1.05 to 5 times, more preferably 1.1 to 4 times. Thestretching may be carried out at a single step or at multi-steps. Theabove Tg when a film obtained by the solution casting method isstretched refers to a glass transition temperature of the above filmcontaining a very small amount of a solvent.

(Chromatic Dispersion)

The optical film of this invention has a feature that the in-planeretardation of the film in the visible light region of wavelengths of400 to 800 nm decreases with a decrease in wavelength. That is, the filmsatisfies the following expression (1).R(450)<R(550)<R(650)  (1)

in which R(450), R(550) and R(650) are in-plane retardation values ofthe film at wavelengths of 450 nm, 550 nm and 650 nm, respectively.

The above in-plane retardation value is defined by the followingexpression, and it is a feature that shows a retardation in phasebetween X direction in which light is transmitted at right angles withthe film and Y direction perpendicular thereto.R=(n _(x) −n _(y))×d

in which n_(x) is a refractive index of in-plane of the film in the mainstretching direction, n_(y) is a refractive index perpendicular to themain stretching direction of in-plane of the film and d is a thicknessof the film. The above main stretching direction refers to a stretchingdirection when monoaxial stretching is carried out, and refers to astretching direction in which the stretching is carried out to increasethe stretch degree more when biaxial stretching is carried out, and itrefers to an orientation direction of a polymer chain as far as achemical structure is concerned.

(Thickness, Etc.)

The thickness of the optical film of this invention is preferably in therange of 20 to 200 μm, more preferably in the range of 20 to 150 μm.When the thickness is in this range, a retardation value desired can beeasily obtained by the stretching, and, preferably, it is easy to formthe film.

In the optical film of this invention, the photoelastic constant of thecopolycarbonate constituting the film is low. Therefore, a change inphase difference against a stress is small, and a liquid crystal displayhaving such a retardation film is excellent in display stability.

The optical film of this invention has high transparency. The totallight transmittance of the 100 μm thick optical film of this inventionis preferably 85% or more, more preferably 88% or more. The haze valueof the optical film of this invention is preferably 5% or less, morepreferably 3% or less.

The film of this invention can be used as a retardation film. Thisinvention includes a liquid crystal display having the above retardationfilm. This invention includes a circularly polarizing film formed of thefilm of this invention and a polarizing layer. This invention includes adisplay device using the above circularly polarizing film as ananti-reflection film.

PREFERRED EMBODIMENTS

The film of this invention includes the following films (I) to (VI) aspreferred embodiments.

(Films (I), (III) and (V))

The films (I), (III) and (V) are films comprising the unit (A2) of thefollowing formula and at least one unit (Bi) selected from the units ofthe following formulae (B1) to (B4).

(Film (I))(Compositional Ratio)

The copolycarbonate for the film (I) preferably contains 25 mol % ormore but less than 40 mol % of the unit (A2) and over 60 mol % but 75mol % or less of at least one unit (Bi) selected from the units of theformulae (B1) to (B4), and has a photoelastic constant absolute value of25×10⁻¹² Pa⁻¹ or less. The copolycarbonate more preferably contains 30mol % or more but less than 40 mol % of the unit (A2) and over 60 mol %but 70 mol % or less of at least one unit (Bi) selected from the unitsof the formulae (B1) to (B4). The copolycarbonate still more preferablycontains over 30 mol % but less than 40 mol % of the unit (A2) and over60 mol % but less than 70 mol % of at least one unit (Bi) selected fromthe units of the formulae (B1) to (B4).

(Chromatic Dispersion)

The film (I) is a film that satisfies the following expressions (2) and(3),0<R(450)/R(550)<1  (2)1.01<R(650)/R(550)<2  (3)and that exhibits a so-called inverse chromatic dispersion. The film (I)is suitably used as a retardation film in a liquid crystal display.

The film (I) more preferably satisfies the following conditions.0.6<R(450)/R(550)<1  (2-1)1.01<R(650)/R(550)<1.40  (3-1)

The film (I) still more preferably satisfies the following conditions.0.65<R(450)/R(550)<0.92  (2-2)1.01<R(650)/R(550)<1.30  (3-2)

The film (I) particularly preferably satisfies the following conditions.0.7<R(450)/R(550)<0.91  (2-3)1.03<R(650)/R(550)<1.20  (3-3)

The film in-plane retardation value R(550) of the film (I) at awavelength of 550 nm is preferably R(550)>50 nm. The film (I) can beused as a λ/4 film or λ/2 film in a broad band in the form of a singlelayer without stacking layers. In such a use, desirably, the λ/4 filmsatisfies 100 nm<R(550)<180 nm, and the λ/2 film satisfies 220nm<R(550)<330 nm.

The film (I) preferably satisfies the following expressions (8) to (10).|R(400)/R(550)−400/550|<0.15  (8)|R(700)/R(550)−700/550|<0.25  (9)|R(400)/R(550)−400/550|² +|R(700)/R(550)−700/550|²<0.05  (10)

wherein R(400), R(550) and R(700) are film in-plane retardation valuesat the wavelengths of 400 nm, 550 nm and 700 nm, respectively.

The film (I) more preferably satisfies the following expressions (8)′,(9)′ and (10)′.|R(400)/R(550)−400/550|<0.10  (8)′|R(700)/R(550)−700/550|<0.23  (9)′|R(400)/R(550)−400/550|² +|R(700)/R(550)−700/550|²<0.047  (10)′

The film (I) still more preferably satisfies the following expressions(8)″, (9)″ and (10)″.|R(400)/R(550)−400/550|<0.05  (8)″|R(700)/R(550)−700/550|<0.21  (9)″|R(400)/R(550)−400/550|² +|R(700)/R(550)−700/550|²<0.045  (10)″

The above expressions (8), (9) and (10) are expressions for attaining abroader band of the retardation film. For attaining a broader band, itis required to satisfy the following expression in a broad range ofvisible light,R(λ)=cλ

wherein R(λ) is a retardation value (nm) at a measurement wavelengthλ(nm), c is a constant of c>0, and the range of λ is 400 nm≦λ≦800 nm. Awavelength of 400 nm is used as an index on the short wavelength side,and a wavelength of 700 nm is used as an index on the long wavelengthside.

The film (I) satisfying the expressions (8), (9) and (10) is excellentin visibility since black under crossed Nicols in a reflection mode isintensified.

When |R(400)/R(550)−400/550| is 0.15 or more, a light omission takesplace on the short wavelength side, which is a problem. When|R(700)/R(550)−700/550| is 0.25 or more, a light omission takes place onthe long wavelength side, which is a problem. Further, when|R(400)/R(550)−400/550|²+|R(700)/R(550)−700/550|² is 0.05 or more, alight omission takes place in the visible light region.

The film in-plane retardation value R(550) of the above film at awavelength of 550 nm is preferably R(550)>50 nm. The above film can beused as a λ/4 film or λ/2 film in a broad band in the form of a singlelayer without stacking layers. In such a use, desirably, the λ/4 filmsatisfies 100 nm<R(550)<180 nm, and the λ/2 film satisfies 220nm<R(550)<330 nm.

The chromatic dispersion is measured by taking a 100 mm long and 70 mmwide test piece from a film, stretching it 2.0 times in the machinedirection at a stretching temperature of Tg+10° C. and measuring theresultant film with a spectroellipsometer M-220 supplied by JASCOCorporation.

(Retardation Exhibition Capability)

The retardation exhibition capability (Δn) of the film (I) satisfies thefollowing expression (11).0.3>Δn>0.003  (11)

(Δn=R(550)(nm)/thickness (nm))

More preferably, it satisfies the following expression (11)′.0.1>Δn>0.0033  (11)′

Still more preferably, it satisfies the following expression (11)″.0.05>Δn>0.0037  (11)″

When the retardation exhibition capability Δn is 0.0037 or more,preferably, the thickness of a λ/4 film can be decreased, and as aresult, the thickness of a display can be decreased.

(Film (III))

(Compositional Ratio)

The copolycarbonate for the film (III) preferably contains 40 mol % ormore but less than 60 mol % of the unit (A2) and over 40 mol % but 60mol % or less of at least one unit (Bi) selected from the units of theformulae (B1) to (B4) and has a photoelastic constant absolute value of25×10⁻¹² Pa⁻¹ or less. The copolycarbonate more preferably contains 45to 55 mol of the unit (A2) and 55 to 45 mol % of at least one unit (Bi)selected from the units of the formulae (B1) to (B4).

(Chromatic Dispersion)

The film (III) satisfies the conditions of the following (4) to (6).−30<R(450)<0  (4)−10<R(550)<10  (5)0<R(650)<30  (6)

The film (III) more preferably satisfies the following conditions.−20<R(450)<0  (4-1)−5<R(550)<5  (5-1)0<R(650)<20  (6-1)

The film (III) is excellent in transparency. The film (III) has a lowoptical anisotropy. That is, the film in-plane retardation value of thefilm (III) at a wavelength of 400 to 800 nm is nearly zero. Therefore,the film (III) can be used as a protective film for a polarizing film ofa liquid crystal display.

(Film (V))

(Compositional Ratio)

The copolycarbonate for the film (V) preferably contains 60 to 90 mol %of the unit (A2) and 10 to 40 mol % of at least one unit (Bi) selectedfrom the units of the formulae (B1) to (B4) and has a photoelasticconstant absolute value of 30×10⁻¹² Pa⁻¹ or less. The copolycarbonatemore preferably contains 65 to 90 mol % of the unit (A2) and 10 to 35mol % of at least one unit (Bi) selected from the units of the formulae(B1) to (B4).

(Chromatic Dispersion)

The film (V) preferably satisfies the following conditions.R(450)<R(550)<R(650)<0  (7)(Retardation Exhibition Capability)

The retardation exhibition capability (Δn) of the film (V) satisfies thefollowing expression (12).−0.001>Δn>−0.3  (12)

(Δn=R(550)(nm)/thickness (nm))

More preferably, it satisfies the following expression (12)′.−0.0015>Δn>−0.05  (12)′

Having a negative birefringence property, the film (V) is suitable as aretardation film for an in-plane switching (IPS) mode liquid crystaldisplay.

(Films (II), (IV) and (VI))

The films (II), (IV) and (VI) are films comprising the unit (A4) of thefollowing expression and at least one unit (Bi) selected from the unitsof the following formulae (B1) to (B4).

(Film (II))(Compositional Ratio)

The copolycarbonate for the film (II) preferably contains 25 mol % ormore but less than 65 mol % of the unit (A4) and over 35 mol % but 75mol % or less of at least one unit (B1) selected from the units of theformulae (B1) to (B4) and has a photoelastic constant absolute value of25×10⁻¹² Pa⁻¹ or less. The copolycarbonate more preferably contains 30to 60 mol % of the unit (A4) and 40 to 70 mol % of at least one unit(B1) selected from the units of the formulae (B1) to (B4).

(Retardation Exhibition Capability)

The film (II) is a film that satisfies the following expressions (2) and(3) and that exhibits a so-called inverse chromatic dispersion.0<R(450)/R(550)<1  (2)1.01<R(650)/R(550)<2  (3)

The film (II) is suitably used as a retardation film for a liquidcrystal display.

The film (II) more preferably satisfies the following conditions.0.6<R(450)/R(550)<1  (2-1)1.01<R(650)/R(550)<1.40  (3-1)

The film (II) still more preferably satisfies the following conditions.0.65<R(450)/R(550)<0.92  (2-2)1.01<R(650)/R(550)<1.30  (3-2)

The film (II) particularly preferably satisfies the followingconditions.0.7<R(450)/R(550)<0.91  (2-3)1.03<R(650)/R(550)<1.20  (3-3)

The film (II) preferably satisfies the following expressions (8) to(10).|R(400)/R(550)−400/550|<0.15  (8)|R(700)/R(550)−700/550|<0.25  (9)|R(400)/R(550)−400/550|² +|R(700)/R(550)−700/550|²<0.05  (10)

wherein R(400), R(550) and R(700) are film in-plane retardation valuesat the wavelengths of 400 nm, 550 nm and 700 nm, respectively.

The film (II) more preferably satisfies the following expressions (8)′,(9)′ and (10)′.|R(400)/R(550)−400/550|<0.10  (8)′|R(700)/R(550)−700/550|<0.23  (9)′|R(400)/R(550)−400/550|² +|R(700)/R(550)−700/550|²<0.047  (10)′

The film (II) still more preferably satisfies the following expressions(8)″, (9)″ and (10)″.|R(400)/R(550)−400/550|<0.05  (8)″|R(700)/R(550)−700/550|<0.21  (9)″|R(400)/R(550)−400/550|² +|R(700)/R(550)−700/550|²<0.045  (10)″(Retardation Exhibition Capability)

The retardation exhibition capability (Δn) of the film (II) satisfiesthe following expression.0.3>Δn>0.002

(Δn=R(550)(nm)/thickness (nm))

More preferably, it satisfies the following expression (11)′.0.1>Δn>0.002

Still more preferably, it satisfies the following expression (11)″.0.05>Δn>0.0023(Film (IV))(Compositional Ratio)

The copolycarbonate for the film (IV) preferably contains 65 mol % ormore but less than 82 mol % of the unit (A4) and over 18 mol % but 35mol % or less of at least one unit (Bi) selected from the units of theformulae (B1) to (B4) and has a photoelastic constant absolute value of25×10⁻¹² Pa⁻¹ or less. The copolycarbonate more preferably contains 65to 80 mol % of the unit (A4) and 20 to 35 mol % of at least one unit(Bi) selected from the units of the formulae (Bi) to (B4).

(Chromatic Dispersion)

The film (IV) satisfies the conditions of the following (4) to (6).−30<R(450)<0  (4)−10<R(550)<10  (5)0<R(650)<30  (6)

The film (IV) more preferably satisfies the following conditions.−20<R(450)<0  (4-1)−5<R(550)<5  (5-1)0<R(650)<20  (6-1)

The film (IV) is excellent in transparency. The film (IV) has a lowoptical anisotropy. That is, the film in-plane retardation value of thefilm (IV) at a wavelength of 400 to 800 nm is nearly zero. Therefore,the film (IV) can be used as a protective film for a polarizing film ofa liquid crystal display.

(Film (VI))

(Compositional Ratio)

The copolycarbonate for the film (VI) preferably contains 82 to 90 mol %of the unit (A4) and over 10 to 18 mol % of at least one unit (Bi)selected from the units of the formulae (B1) to (B4) and has aphotoelastic constant absolute value of 30×10⁻¹² Pa⁻¹ or less.

(Chromatic Dispersion)

The film (VI) preferably satisfies the following condition.R(450)<R(550)<R(650)<0  (7)(Retardation Exhibition Capability)

The retardation exhibition capability (Δn) of the film (VI) preferablysatisfies the following expression (12).−0.001>Δn>−0.3  (12)

(Δn=R(550)(nm)/thickness (nm))

Having a negative birefringence property, the film (VI) is suitable as aretardation film for an in-plane switching (IPS) mode liquid crystaldisplay.

(Use)

The optical film of this invention is used for a retardation film, aplastic cell substrate film, a protective film for a polarizing film, ananti-reflection film, a brightness increasing film, a protective filmfor an optical disk and a diffusion film. In particular, it is preferredfor a retardation film, a protective film for a polarizing film and ananti-reflection film.

EXAMPLES

This invention will be explained in detail hereinafter with reference toExamples, while this invention shall not be limited thereto. InExamples, “part” stands for “part by weight”. Resins used in Examplesand evaluation methods are as follows.

1. Photoelastic Constant Measurement

A 50 mm long and 10 mm wide test piece was taken from a central portionof a film, and measured for a photoelastic constant with aspectroellipsometer M-220 supplied by JASCO Corporation.

2. Retardation and Chromatic Dispersion Measurements

A 100 mm long and 70 mm wide test piece was taken from a central portionof a film and stretched 2.0 times in the machine direction at astretching temperature of Tg+10° C., and the thus-obtained film was fora retardation and chromatic dispersion with a spectroellipsometer M-220supplied by JASCO Corporation.

3. Tg (Glass Transition Temperature) Measurement

Measured with a 2910 type DSC supplied by T. A. Instruments Japan in anitrogen atmosphere at a temperature elevation rate of 20° C./minute.

4. Polymer Compositional Ratio (NMR)

Measurement was made with a proton NMR of JNM-AL400 supplied by JEOLLtd, and a polymer compositional ratio was calculated.

5. Viscosity Average Molecular Weight

0.7 gram of a copolycarbonate was dissolved in 100 mL of methylenechloride, and measured for a specific viscosity in a solution at 20° C.,and the specific viscosity (η_(sp)) was inserted into the followingequation to determine a viscosity average molecular weight.η_(sp) /c=[η]+0.45×[η]2c(in which [η] is an intrinsic viscosity)[η]=1.23×10⁻⁴M^(0.83)c=0.76. Contrast Evaluation

Polarizing films on both the sides of a commercially availablereflection type VA liquid crystal panel were peeled off, an opticalanisotropy layer formed of a liquid crystal was formed on a preparedfilm, a polarizing film was stacked thereon, and the resultant stack wasbonded with an adhesive such that the optical anisotropy layer of theprepared film was placed on the panel side, to obtain a liquid crystalpanel. A display screen of the above liquid crystal panel duringreflection was evaluated for a contrast and determined as ◯, Δ or X inthe order of from being good to being poor.

Example 1

<Production of Copolycarbonate>

72.32 Parts of isosorbide (to be abbreviated as “ISS” hereinafter),80.24 parts of 9,9-bis(4-hydroxy-3-methylphenyl)fluorene (to beabbreviated as “BCF” hereinafter), 154.61 parts of diphenyl carbonateand 1.8×10⁻² part of tetramethylammonium hydroxide and 1.6×10⁻⁴ part ofsodium hydroxide as catalysts were heated and melted at 180° C. undernitrogen atmosphere. Then, the degree of reduced pressure was adjustedto 13.4 kPa over 30 minutes. Then, the temperature was elevated to 260°C. at a rate of 60° C./hour, and it was maintained at this temperaturefor 10 minutes. Then, the degree of reduced pressure was adjusted to 133Pa or lower over a period of 1 hour. The reaction was carried out withstirring for a total time period of 6 hours.

After completion of the reaction, dodecylbenzenesulfonic acidtetrabutylphosphonium salt having a molar amount 4 times the catalystamount was added to deactivate the catalysts, and a reaction product wasdischarged from the bottom of the reactor under elevated pressure bynitrogen and cut with a pelletizer while it was cooled in a watervessel, to give pellets. The resultant pellets had a viscosity averagemolecular weight of 19,600. A compositional ratio was measured on thebasis of NMR. The composition ratio was BCF/ISS=29.8/70.2, and thedeviation thereof from the charged amount ratio was as small as 0.2.

<Production of Optical Film>

Then, a T-die having a lip width of 500 μm and a film take-up apparatuswere attached to a 15 mmφ twin-screw extruder supplied by TECHNOVELCORPORATION, and the obtained copolycarbonate was molded into a film toobtain a transparent extrusion film. A sample having a size of 50 mm×10mm was taken from a central portion having a thickness of 68±0.8 μm inthe obtained film, and the sample was measured for a photoelasticconstant and a Tg. Further, a 100 mm long and 70 mm wide sample taken inthe same manner was monoaxially stretched 2.0 times in the lengthdirection at 196° C. (Tg+10° C.) to give a stretched film having alength of 200 mm, a width of 56 mm and a thickness of 49 μm. Thestretched film was measured for a retardation and chromatic dispersion.Further, the contrast evaluation was carried out. The deviation of thecompositional ratio from the charged amount ratio was as small as 0.2,and the chromatic dispersion was hence not affected. Table 1 shows theresults.

Example 2

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 68.19 parts of ISS, 90.94 parts of BCF and154.61 parts of diphenyl carbonate were used. The thus-obtained pelletshad a viscosity average molecular weight of 19,200. Its compositionalratio was measured on the basis of NMR. The compositional ratio wasBCF/ISS=33.7/67.3, and the deviation thereof from the charged amountratio was as small as 0.3.

<Production of Optical Film>

The copolycarbonate was dissolved in methylene chloride to prepare adope having a solid content of 19% by weight. A cast film (thickness68±0.8 μm) was formed from the dope by a known method. A sample having asize of 50 mm×10 mm was taken from a 80±0.8 μm thick portion in thevicinity of the center of the thus-obtained film, and the sample wasevaluated for a photoelastic coefficient and a Tg in the same manner asin Example 1. A film taken in the same manner as in Example 1 wasmonoaxially stretched 2.0 times at Tg+10° C. in the same manner as inExample 1 to obtain a stretched film having a length of 200 mm, a widthof 57 mm and a thickness of 48 μm. Since the deviation of thecompositional ratio from the charged amount ratio was as small as 0.2,the chromatic dispersion was not affected. The stretched film wasmeasured for a retardation and chromatic dispersion in the same manneras in Example 1. Further, the contrast evaluation was also carried out.Table 1 shows the results.

Example 3

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 72.32 parts of ISS, 93.09 parts of9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (to be abbreviated as “BPEF”hereinafter) and 154.61 parts of diphenyl carbonate were used. Thethus-obtained pellets had a viscosity average molecular weight of19,600. Its compositional ratio was measured on the basis of NMR. Thecompositional ratio was BPEF/ISS=29.8/70.2, and the deviation thereoffrom the charged amount ratio was as small as 0.2.

<Production of Optical Film>

A film (thickness 83±0.8 μm) was prepared in the same manner as inExample 1. The obtained film was evaluated for a photoelastic constantand a Tg in the same manner as in Example 1. A film taken in the samemanner as in Example 1 was monoaxially stretched 2.0 times at Tg+10° C.in the same manner as in Example 1 to obtain a stretched film having alength of 200 mm, a width of 57 mm and a thickness of 64 μm. Thestretched film was measured for a retardation and chromatic dispersion.Further, the contrast evaluation was also carried out. Since thedeviation of the compositional ratio from the charged amount ratio wasas small as 0.2, the chromatic dispersion was not affected. Table 1shows the results.

Example 4

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 61.99 parts of ISS, 124.12 parts of BPEF 154.61parts of diphenyl carbonate were used. The thus-obtained pellets had aviscosity average molecular weight of 19,400. Its compositional ratiowas measured on the basis of NMR. The compositional ratio wasBPEF/ISS=39.8/60.2, and the deviation thereof from the charged amountratio was as small as 0.2.

<Production of Optical Film>

A film (thickness 84±0.8 μm) was prepared in the same manner as inExample 1. The obtained film was evaluated for a photoelastic constantand a Tg in the same manner as in Example 1. A film taken in the samemanner as in Example 1 was monoaxially stretched 2.0 times at Tg+10° C.in the same manner as in Example 1 to obtain a stretched film having alength of 200 mm, a width of 57 mm and a thickness of 64 μm. Thestretched film was measured for a retardation and chromatic dispersion.Further, the contrast evaluation was also carried out. Since thedeviation of the compositional ratio from the charged amount ratio wasas small as 0.2, the chromatic dispersion was not affected. Table 1shows the results.

Example 5

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 51.66 parts of ISS, 155.15 parts of BPEF and154.61 parts of diphenyl carbonate were used. The thus-obtained pelletshad a viscosity average molecular weight of 19,000. Its compositionalratio was measured on the basis of NMR. The compositional ratio wasBPEF/ISS=49.8/50.2, and the deviation thereof from the charged amountratio was as small as 0.2.

<Production of Optical Film>

A film (thickness 82±0.8 μm) was prepared in the same manner as inExample 1. The obtained film was evaluated for a photoelastic constantand a Tg in the same manner as in Example 1. A film taken in the samemanner as in Example 1 was monoaxially stretched 2.0 times at Tg+10° C.in the same manner as in Example 1 to obtain a stretched film having alength of 200 mm, a width of 57 mm and a thickness of 62 μm. Thestretched film was measured for a retardation and chromatic dispersion.Further, the contrast evaluation was also carried out. Since thedeviation of the compositional ratio from the charged amount ratio wasas small as 0.2, the chromatic dispersion was not affected. Table 1shows the results.

Example 6

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 41.33 parts of ISS, 186.18 parts of BPEF and154.61 parts of diphenyl carbonate were used. The thus-obtained pelletshad a viscosity average molecular weight of 19,200. Its compositionalratio was measured on the basis of NMR. The compositional ratio wasBPEF/ISS=59.7/40.3, and the deviation thereof from the charged amountratio was as small as 0.3.

<Production of Optical Film>

A film (thickness 83±0.8 μm) was prepared in the same manner as inExample 1. The obtained film was evaluated for a photoelastic constantand a Tg in the same manner as in Example 1. A film taken in the samemanner as in Example 1 was monoaxially stretched 2.0 times at Tg+10° C.in the same manner as in Example 1 to obtain a stretched film having alength of 200 mm, a width of 57 mm and a thickness of 63 μm. Thestretched film was measured for a retardation and chromatic dispersion.Further, the contrast evaluation was also carried out. Since thedeviation of the compositional ratio from the charged amount ratio wasas small as 0.3, the chromatic dispersion was not affected. Table 1shows the results.

Example 7

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 51.66 parts of ISS, 133.74 parts of BCF and154.61 parts of diphenyl carbonate were used. The thus-obtained pelletshad a viscosity average molecular weight of 18,900.

<Production of Optical Film>

The copolycarbonate was dissolved in methylene chloride to prepare adope having a solid content of 19% by weight. A cast film (thickness81±0.8 μm) was formed from the dope by a known method. The thus-obtainedfilm was evaluated for a photoelastic coefficient and a Tg in the samemanner as in Example 1. A film taken in the same manner as in Example 1was monoaxially stretched 2.0 times at Tg+10° C. in the same manner asin Example 1 to obtain a stretched film having a length of 200 mm, awidth of 57 mm and a thickness of 62 μm. The stretched film was measuredfor a retardation and chromatic dispersion in the same manner as inExample 1. Table 2 shows the results.

Example 8

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 30.99 parts of ISS, 217.21 parts of BPEF and154.61 parts of diphenyl carbonate were used. The thus-obtained pelletshad a viscosity average molecular weight of 19,000.

<Production of Optical Film>

A film (thickness 83±0.8 μm) was formed in the same manner as inExample 1. The thus-obtained film was evaluated for a photoelasticcoefficient and a Tg in the same manner as in Example 1. A film taken inthe same manner as in Example 1 was monoaxially stretched 2.0 times atTg+10° C. in the same manner as in Example 1 to obtain a stretched filmhaving a length of 200 mm, a width of 57 mm and a thickness of 63 μm.The stretched film was measured for a retardation and chromaticdispersion. Table 2 shows the results.

Example 9

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 20.66 parts of ISS, 248.24 parts of BPEF and154.61 parts of diphenyl carbonate were used. The thus-obtained pelletshad a viscosity average molecular weight of 19,200.

<Production of Optical Film>

A film (thickness 81±0.8 μm) was formed in the same manner as inExample 1. The thus-obtained film was evaluated for a photoelasticcoefficient and a Tg in the same manner as in Example 1. A film taken inthe same manner as in Example 1 was monoaxially stretched 2.0 times atTg+10° C. in the same manner as in Example 1 to obtain a stretched filmhaving a length of 200 mm, a width of 57 mm and a thickness of 62 μm.The stretched film was measured for a retardation and chromaticdispersion. Table 2 shows the results.

Example 10

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 15.5 parts of ISS, 227.36 parts of BCF and154.61 parts of diphenyl carbonate were used. The thus-obtained pelletshad a viscosity average molecular weight of 16,500.

<Production of Optical Film>

The copolycarbonate was dissolved in methylene chloride to prepare adope having a solid content of 19% by weight. A cast film (thickness80±0.8 μm) was formed from the dope by a known method. The thus-obtainedfilm was evaluated for a photoelastic coefficient and a Tg in the samemanner as in Example 1. A film taken in the same manner as in Example 1was monoaxially stretched 2.0 times at Tg+10° C. in the same manner asin Example 1 to obtain a stretched film having a length of 200 mm, awidth of 57 mm and a thickness of 63 μm. The stretched film was measuredfor a retardation and chromatic dispersion. Table 3 shows the results.

Example 11

<Production of Copolycarbonate>

An aromatic-aliphatic copolycarbonate was obtained in the same manner asin Example 1 except that 10.33 parts of ISS, 279.27 parts of BPEF and154.61 parts of diphenyl carbonate were used. The thus-obtained pelletshad a viscosity average molecular weight of 19,200.

<Production of Optical Film>

A film (thickness 85±0.8 μm) was formed in the same manner as inExample 1. The thus-obtained film was evaluated for a photoelasticcoefficient and a Tg in the same manner as in Example 1. A film taken inthe same manner as in Example 1 was monoaxially stretched 2.0 times atTg+10° C. in the same manner as in Example 1 to obtain a stretched filmhaving a length of 200 mm, a width of 57 mm and a thickness of 65 μm.The stretched film was measured for a retardation and chromaticdispersion. Table 3 shows the results.

Comparative Example 1

<Production of Aromatic Polycarbonate>

A reactor having a thermometer, a stirrer and a reflux condenser wascharged with 9,809 parts of deionized water and 2,271 parts of a 48%sodium hydroxide aqueous solution, 1,775 parts of2,2-bis(4-hydroxyphenyl)propane (BPA) and 3.5 parts of sodiumhydrosulfite were dissolved therein, 7,925 parts of methylene chloridewas added, and then 1,000 parts of phosgene was blown into it withstirring at 16 to 20° C. over a period of 60 minutes. After completionof the blowing of the phosgene, 52.6 parts of p-tert-butylphenol and 327parts of a 48% sodium hydroxide aqueous solution were added, 1.57 partsof triethylamine was added, and the mixture was stirred at 20 to 27° C.for 40 minutes to complete the reaction. A methylene chloride layercontaining a formed product was washed with dilute hydrochloric acid andpure water, and then methylene chloride was evaporated off to give anaromatic polycarbonate. The resultant powder had a viscosity averagemolecular weight of 15,500.

<Production of Optical Film>

The thus-obtained aromatic polycarbonate was pelletized with a 15 mmφtwin-screw extruder. Then, a film (thickness 58±0.8 μm) was formed inthe same manner as in Example 1. The obtained film was evaluated for aphotoelastic constant and a Tg in the same manner as in Example 1. Afilm taken in the same manner as in Example 1 was monoaxially stretched2.0 times at Tg+10° C. in the same manner as in Example 1 to obtain astretched film having a length of 200 mm, a width of 56 mm and athickness of 41 μm. The stretched film was measured for a retardationand chromatic dispersion. Tables 1 and 2 show the results. Further, thecontrast evaluation was carried out. Tables 1 and 2 show the results.This film had a high photoelastic constant of 80×10⁻¹² Pa⁻¹, and hadlarge birefringence caused by a stress. When the film is used as aretardation film, undesirably, a light omission hence takes place.Further, since the chromatic dispersion thereof is positive dispersion,λ/4 is not attainable in a broad band, and there is caused the problemof a color omission.

Comparative Example 2

<Production of Aromatic Copolycarbonate>

A reactor having a thermometer, a stirrer and a reflux condenser wascharged with 9,809 parts of deionized water and 2,271 parts of a 48%sodium hydroxide aqueous solution, 585 parts of2,2-bis(4-hydroxyphenyl)propane (BPA), 1,969 parts of9,9-bis(4-hydroxy-3-methylphenyl)fluorene and 4.5 parts of sodiumhydrosulfite were dissolved therein, 6,604 parts of methylene chloridewas added, and then 1,000 parts of phosgene was blown into it withstirring at 16 to 20° C. over a period of 60 minutes. After completionof the blowing of the phosgene, 70 parts of p-tert-butylphenol and 327parts of a 48% sodium hydroxide aqueous solution were added, 1.57 partsof triethylamine was further added, and the mixture was stirred at 20 to27° C. for 40 minutes to complete the reaction. A methylene chloridelayer containing a formed product was washed with dilute hydrochloricacid and pure water, and then methylene chloride was evaporated off togive an aromatic copolycarbonate having a fluorene structure. Theresultant powder had a viscosity average molecular weight of 38,200. Itscompositional ratio was measured on the basis of NMR. The compositionalratio was BPA/BCF=32.8/67.2, and the deviation thereof from the chargedamount ratio was as small as 0.2.

<Production of Optical Film>

A film (thickness 141±0.8 μm) was formed in the same manner as inExample 2. The obtained film was evaluated for a photoelastic constantand a Tg in the same manner as in Example 1. A film taken in the samemanner as in Example 1 was monoaxially stretched 2.0 times at Tg+10° C.in the same manner as in Example 1 to obtain a stretched film having alength of 200 mm, a width of 56 mm and a thickness of 100 μm. Thestretched film was measured for a retardation and chromatic dispersion.Further, the contrast evaluation was carried out. Since the deviation ofthe compositional ratio from the charged amount ratio was as small as0.2, the chromatic dispersion was not affected. Table 1 shows theresults. This film had a high photoelastic constant of 44×10⁻¹² Pa⁻¹,and had large birefringence caused by a stress. When the film is used asa retardation film, undesirably, a light omission hence takes place.

Comparative Example 3

<Production of Copolycarbonate>

A copolycarbonate was obtained in the same manner as in Example 1 exceptthat 7.67 parts of ISS, 24.2 parts of spiroglycol (to be abbreviated asSPG hereinafter), 6.81 parts of BCF and 32.45 parts of diphenylcarbonate were used. The thus-obtained pellets had a viscosity averagemolecular weight of 16,300. Its compositional ratio was measured on thebasis of NMR. The compositional ratio thereof wasISS/SPG/BCF=34.6/52.6/12.8, and the deviation thereof from the chargedamount ratio was as large as 0.8.

<Production of Optical Film>

A film (thickness 78±0.8 μm) was formed in the same manner as inExample 1. The obtained film was evaluated for a photoelastic constantin the same manner as in Example 1. A film taken in the same manner asin Example 1 was monoaxially stretched 2.0 times at Tg+10° C. in thesame manner as in Example 1 to obtain a stretched film having a lengthof 200 mm, a width of 57 mm and a thickness of 48 μm. The stretched filmwas measured for a retardation and chromatic dispersion. Further, thecontrast evaluation was carried out. Since the deviation of thecompositional ratio from the charged amount ratio was as large as 0.8,it was difficult to control the chromatic dispersion. Table 1 shows theresults.

Comparative Example 4

<Production of Aromatic Copolycarbonate>

A reactor having a thermometer, a stirrer and a reflux condenser wascharged with 9,809 parts of deionized water and 2,271 parts of a 48sodium hydroxide aqueous solution, 461 parts of2,2-bis(4-hydroxyphenyl)propane (BPA), 2,175 parts of9,9-bis(4-hydroxy-3-methylphenyl)fluorene and 4.5 parts of sodiumhydrosulfite were dissolved therein, 6,404 parts of methylene chloridewas added, and then 1,000 parts of phosgene was blown into it withstirring at 16 to 20° C. over a period of 60 minutes. After completionof the blowing of the phosgene, 70 parts of p-tert-butylphenol and 327parts of a 48% sodium hydroxide aqueous solution were added, 1.57 partsof triethylamine was further added, and the mixture was stirred at 20 to27° C. for 40 minutes to complete the reaction. A methylene chloridelayer containing a formed product was washed with dilute hydrochloricacid and pure water, and then methylene chloride was evaporated off togive an aromatic copolycarbonate having a fluorene structure. Itscompositional ratio was measured on the basis of NMR. The resultantpowder had a viscosity average molecular weight of 38,200.

<Production of Optical Film>

A film (thickness 164±0.8 μm) was formed in the same manner as inExample 2. The obtained film was evaluated for a photoelastic constantin the same manner as in Example 1. A film taken in the same manner asin Example 1 was monoaxially stretched 2.0 times at Tg+10° C. in thesame manner as in Example 1 to obtain a stretched film having a lengthof 200 mm, a width of 56 mm and a thickness of 100 μm. The stretchedfilm was measured for a retardation and chromatic dispersion. Table 2shows the results. This film had a high photoelastic constant of42×10⁻¹² Pa⁻¹, and had large birefringence caused by a stress. When thefilm is used as a retardation film, undesirably, a light omission hencetakes place.

Comparative Example 5

<Production of Copolycarbonate>

A reactor having a thermometer, a stirrer and a reflux condenser wascharged with 9,809 parts of deionized water and 2,271 parts of a 48%sodium hydroxide aqueous solution, 337 parts of2,2-bis(4-hydroxyphenyl)propane (BPA), 2,280 parts of9,9-bis(4-hydroxy-3-methylphenyl)fluorene and 4.5 parts of sodiumhydrosulfite were dissolved therein, 6,404 parts of methylene chloridewas added, and then 1,000 parts of phosgene was blown into it withstirring at 16 to 20° C. over a period of 60 minutes. After completionof the blowing of the phosgene, 70 parts of p-tert-butylphenol and 327parts of a 48% sodium hydroxide aqueous solution were added, 1.57 partsof triethylamine was further added, and the mixture was stirred at 20 to27° C. for 40 minutes to complete the reaction. A methylene chloridelayer containing a formed product was washed with dilute hydrochloricacid and pure water, and then methylene chloride was evaporated off togive an aromatic copolycarbonate having a fluorene structure. Itscompositional ratio was measured on the basis of NMR.

<Production of Optical Film>

A film (thickness 164±0.8 μm) was formed in the same manner as inExample 2. The obtained film was evaluated for a photoelastic constantin the same manner as in Example 1. A film taken in the same manner asin Example 1 was monoaxially stretched 2.0 times at Tg+10° C. in thesame manner as in Example 1 to obtain a stretched film having a lengthof 200 mm, a width of 56 mm and a thickness of 100 μm. The stretchedfilm was measured for a retardation and chromatic dispersion. Table 3shows the results. This film had a high photoelastic constant of38×10⁻¹² Pa⁻¹, and had large birefringence caused by a stress. When thefilm is used as a retardation film, undesirably, a light omission hencetakes place.

TABLE 1 BCF BPEF ISS BPA SPG Tg P(550) R(450)/ R(650)/ mol % mol % mol %mol % mol % ° C. nm R(550) R(550) Example 1 30 — 70 — — 186 195 0.8961.041 Example 2 34 — 66 — — 189 179 0.838 1.081 Example 3 — 30 70 — —159 195 0.984 1.012 Example 4 — 40 60 — — 158 153 0.906 1.035 Example 5— 50 50 — — 157 140 0.835 1.070 Example 6 — 60 40 — — 156 124 0.7061.090 Comparative — — — 100 — 148 248 1.080 0.970 Example 1 Comparative67 — —  33 — 225 178 0.810 1.070 Example 2 Comparative 12 — 35 — 53 138132 0.946 1.014 Example 3 Difference between BCF charged Viscosityamount ratio Photoelastic average and Film constant molecularcompositional forming Contrast 10⁻¹² Pa

n weight ratio method evaluation Example 1 19 0.0040 19600 0.2 Melt film◯ forming method Example 2 20 0.0037 19200 0.3 Casting ◯ method Example3 19 0.0030 19600 0.2 Melt film ◯ forming method Example 4 21 0.002419400 0.2 Melt film ◯ forming method Example 5 23 0.0023 19000 0.2 Meltfilm ◯ forming method Example 6 25 0.0025 19200 0.3 Melt film ◯ formingmethod Comparative 80 0.0060 15500 — Melt film X Example 1 formingmethod Comparative 44 0.0018 38200 0.2 Casting ◯ Example 2 methodComparative 13 0.0028 16300 0.8 Melt film Δ Example 3 forming method

TABLE 2 Viscosity Photoelastic average Film BCF BPEF ISS BPA Tg constantR(450) R(550) R(650) molecular forming mol % mol % mol % mol % ° C.10⁻¹² Pa⁻¹ nm nm nm weight method Example 7 50 — 50 — 199 22 −3 5 818900 Casting method Example 8 — 70 30 — 155 27 −8 0 3 19000 Melt filmforming method Example 9 — 80 20 — 154 28 −11 −3 1 19200 Melt filmforming method Comparative — — — 100 148 80 268 248 241 15500 MeltExample 1 film forming method Comparative 74 — —  26 234 42 −44 0 1638200 Casting Example 4 method

TABLE 3 Viscosity Photoelastic average Film BCF BPEF ISS BPA constantR(450) R(550) R(650) molecular forming mol % mol % mol % mol % 10⁻¹²Pa⁻¹ nm nm nm weight

n method Example 10 85 — 15 — 28 −181 −141 −131 16500 −0.0022 Castingmethod Example 11 — 90 10 — 29 −104 −71 −58 19200 −0.0011 Melt filmforming method Comparative 81 — — 19 38 −118 −100 −95 35200 −0.0010Casting Example 5  method

Referential Example 1

<Production of Aliphatic Polycarbonate>

103.31 Parts of cyclohexanedimethanol (to be abbreviated as CHDMhereinafter), 154.61 parts of diphenyl carbonate and 1.8×10⁻² part oftetramethylammonium hydroxide and 1.6×10⁻⁴ part of sodium hydroxide ascatalysts were heated to 180° C. under nitrogen atmosphere to melt them.Then, the degree of reduced pressure was adjusted to 13.4 kPa over aperiod of 30 minutes. Then, the temperature was increased up to 240° C.at a rate of 60° C./hour, this temperature was maintained for 10minutes, and then the degree of reduced pressure was adjusted to 133 Paor lower over a period of 1 hour. The reaction was carried out withstirring for a total time period of 6 hours.

After completion of the reaction, dodecylbenzenesulfonic acidtetrabutylphosphonium salt in an amount 4 times the catalyst amount wasadded to deactivate the catalysts, then, a reaction product wasdischarged from the bottom of the reaction vessel under nitrogenpressure and cut with a pelletizer with cooling it in a water vessel togive pellets.

<Production of Optical Film>

Then, a T-die having a lip width of 500 μm and a film take-up apparatuswere attached to a 15 mmφ twin-screw extruder supplied by TECHNOVELCORPORATION, and the obtained copolycarbonate was molded into a film toobtain a transparent extrusion film. A sample that was taken from acentral portion of the obtained film was measured for a photoelasticconstant and a viscosity average molecular weight. Further, a samplethat was taken in the same manner was monoaxially stretched 2.0 times inthe length direction at 51° C. (Tg+10° C.) to give a stretched film. Thestretched film was measured for a retardation and chromatic dispersion.Table 4 shows the results.

Referential Example 2

<Production of Aliphatic Polycarbonate>

An aliphatic polycarbonate was obtained in the same manner as inReferential Example 1 except that 138.9 parts oftricyclo[5.2.1.0.2,6]decanedimethanol (to be abbreviated as CDDMhereinafter) and 154.61 parts of diphenyl carbonate were used.

<Production of Optical Film>

Then, a film was formed in the same manner as in Referential Example 1and measured for a photoelastic constant and a viscosity averagemolecular weight. Further, a sample that was taken in the same manner asin Referential Example 1 was monoaxially stretched 2.0 times at Tg+10°C. in the same manner as in Referential Example 1, and the thus-obtainedfilm was measured for a retardation and chromatic dispersion. Table 4shows the results.

Referential Example 3

<Production of Aliphatic Polycarbonate>

An aliphatic polycarbonate was obtained in the same manner as inReferential Example 1 except that 154.47 parts of dioxane glycol (to beabbreviated as DOG hereinafter) and 154.61 parts of diphenyl carbonatewere used.

<Production of Optical Film>

Then, a film was formed in the same manner as in Referential Example 1and measured for a photoelastic constant and a viscosity averagemolecular weight. Further, a sample that was taken in the same manner asin Referential Example 1 was monoaxially stretched 2.0 times at Tg+10°C. in the same manner as in Referential Example 1, and the thus-obtainedfilm was measured for a retardation and chromatic dispersion. Table 4shows the results.

Referential Example 4

<Production of Aliphatic Polycarbonate>

An aliphatic polycarbonate was obtained in the same manner as inReferential Example 1 except that 161.55 parts of bisphenol A (to beabbreviated as BPA hereinafter) and 154.61 parts of diphenyl carbonatewere used.

<Production of Optical Film>

Then, a film was formed in the same manner as in Referential Example 1and measured for a photoelastic constant and a viscosity averagemolecular weight. Further, a sample that was taken in the same manner asin Referential Example 1 was monoaxially stretched 2.0 times at Tg+10°C. in the same manner as in Referential Example 1, and the thus-obtainedfilm was measured for a retardation and chromatic dispersion. Table 4shows the results.

Referential Example 5

<Production of Aromatic Polycarbonate>

A reactor having a thermometer, a stirrer and a reflux condenser wascharged with 9,809 parts of deionized water and 2,271 parts of a 48%sodium hydroxide aqueous solution, 2,939 parts of9,9-bis(4-hydroxy-3-methylphenyl)fluorene (to be abbreviated as BCFhereinafter) and 4.5 parts of sodium hydrosulfite were dissolvedtherein, 6,604 parts of chloroform was added, and then 1,000 parts ofphosgene was blown into it with stirring at 16 to 20° C. over a periodof 60 minutes. After completion of the blowing of the phosgene, 70 partsof p-tert-butylphenol and 327 parts of a 48% sodium hydroxide aqueoussolution were added, 1.57 parts of triethylamine was further added, andthe mixture was stirred at 20 to 27° C. for 40 minutes to complete thereaction. A methylene chloride layer containing a formed product waswashed with dilute hydrochloric acid and pure water, and then methylenechloride was evaporated off to give an aromatic polycarbonate.

<Production of Optical Film>

The copolycarbonate was dissolved in methylene chloride to prepare adope having a solid content of 19% by weight. A cast film was formedfrom the dope by a known method. A sample that was taken from a centralportion of the thus-obtained film was evaluated for a photoelasticcoefficient, a viscosity average molecular weight and a Tg in the samemanner as in Referential Example 1. Further, a film taken in the samemanner as in Referential Example 1 was monoaxially stretched 2.0 timesat Tg+10° C. in the same manner as in Referential Example 1, and thethus-obtained stretched film was measured for a retardation andchromatic dispersion in the same manner as in Referential Example 1.Table 4 shows the results.

Referential Example 6

<Production of Aromatic Polycarbonate>

An aromatic polycarbonate was obtained in the same manner as inReferential Example 1 except that 310.3 parts of9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (to be abbreviated as BPEFhereinafter) and 154.61 parts of diphenyl carbonate were used.

<Production of Optical Film>

Then, a film was formed in the same manner as in Referential Example 1and measured for a photoelastic constant and a viscosity averagemolecular weight. Further, a sample that was taken in the same manner asin Referential Example 1 was monoaxially stretched 2.0 times at Tg+10°C. in the same manner as in Referential Example 1, and the thus-obtainedfilm was measured for a retardation and chromatic dispersion. Table 4shows the results.

Example 12

<Production of Copolycarbonate>

67.35 Parts of CHDM, 90.94 parts of BCF and 154.61 parts of diphenylcarbonate and 1.8×10⁻² part of tetramethylammonium hydroxide and1.6×10⁻⁴ part of sodium hydroxide as catalysts were heated to 180° C.under nitrogen atmosphere to melt them. Then, the degree of reducedpressure was adjusted to 13.4 kPa over a period of 30 minutes. Then, thetemperature was increased up to 260° C. at a rate of 60° C./hour, thistemperature was maintained for 10 minutes, and then the degree ofreduced pressure was adjusted to 133 Pa or lower over a period of 1hour. The reaction was carried out with stirring for a total time periodof 6 hours.

After completion of the reaction, dodecylbenzenesulfonic acidtetrabutylphosphonium salt in an amount 4 times the catalyst amount wasadded to deactivate the catalysts, then, a reaction product wasdischarged from the bottom of the reaction vessel under nitrogenpressure and cut with a pelletizer with cooling it in a water vessel togive pellets.

<Production of Optical Film>

Then, a T-die having a lip width of 500 μm and a film take-up apparatuswere attached to a 15 mmφ twin-screw extruder supplied by TECHNOVELCORPORATION, and the obtained copolycarbonate was molded into a film toobtain a transparent extrusion film. A sample that was taken from acentral portion of the obtained film was measured for a photoelasticconstant and a viscosity average molecular weight. Further, a samplethat was taken in the same manner was monoaxially stretched 2.0 times inthe length direction at 126° C. (Tg+10° C.) to give a stretched film.The stretched film was measured for a retardation and chromaticdispersion. Table 5 shows the results.

Example 13

<Production of Copolycarbonate>

A copolycarbonate was obtained in the same manner as in Example 12except that 91.68 parts of TCDDM, 90.94 parts of BCF and 154.61 parts ofdiphenyl carbonate were used.

<Production of Optical Film>

Then, a film was formed in the same manner as in Example 12, andmeasured for a photoelastic constant and a viscosity average molecularweight. Further, a sample that was taken in the same manner as inExample 12 was monoaxially stretched 2.0 times at Tg+10° C. in the samemanner as in Example 12, and the thus-obtained stretched film wasmeasured for a retardation and chromatic dispersion. Table 5 shows theresults.

Example 14

<Production of Copolycarbonate>

A copolycarbonate was obtained in the same manner as in Example 12except that 69.45 parts of TCDDM, 155.15 parts of BPEF and 154.61 partsof diphenyl carbonate were used.

<Production of Optical Film>

Then, a film was formed in the same manner as in Example 12, andmeasured for a photoelastic constant and a viscosity average molecularweight. Further, a sample that was taken in the same manner as inExample 12 was monoaxially stretched 2.0 times at Tg+10° C. in the samemanner as in Example 12, and the thus-obtained stretched film wasmeasured for a retardation and chromatic dispersion. Table 5 shows theresults.

Example 15

<Production of Copolycarbonate>

A copolycarbonate was obtained in the same manner as in Example 12except that 101.95 parts of DOG, 90.94 parts of BCF and 154.61 parts ofdiphenyl carbonate were used.

<Production of Optical Film>

Then, a film was formed in the same manner as in Example 12, andmeasured for a photoelastic constant and a viscosity average molecularweight. Further, a sample that was taken in the same manner as inExample 12 was monoaxially stretched 2.0 times at Tg+10° C. in the samemanner as in Example 12, and the thus-obtained stretched film wasmeasured for a retardation and chromatic dispersion. Table 5 shows theresults.

Comparative Example 6

<Production of Copolycarbonate>

A reactor having a thermometer, a stirrer and a reflux condenser wascharged with 9,809 parts of deionized water and 2,271 parts of a 48%sodium hydroxide aqueous solution, 585 parts of BPA, 1,969 parts of BCFand 4.5 parts of sodium hydrosulfite dissolved therein, 6,604 parts ofmethylene chloride was added, and then 1,000 parts of phosgene was blowninto it with stirring at 16 to 20° C. over a period of 60 minutes. Aftercompletion of the blowing of the phosgene, 70 parts ofp-tert-butylphenol and 327 parts of a 48% sodium hydroxide aqueoussolution were added, 1.57 parts of triethylamine was further added, andthe mixture was stirred at 20 to 27° C. for 40 minutes to complete thereaction. A methylene chloride layer containing a formed product waswashed with dilute hydrochloric acid and pure water, and then methylenechloride was evaporated off to give a copolycarbonate having a fluorenestructure.

<Production of Optical Film>

The copolycarbonate was dissolved in methylene chloride to prepare adope having a solid content of 19% by weight. A cast film was formedfrom the dope by a known method. A sample that was taken from a centralportion of the thus-obtained film was evaluated for a photoelasticcoefficient, a viscosity average molecular weight and a Tg in the samemanner as in Referential Example 1. Further, a film taken in the samemanner as in Referential Example 1 was monoaxially stretched 2.0 timesat Tg+10° C. in the same manner as in Referential Example 1, and thethus-obtained stretched film was measured for a retardation andchromatic dispersion in the same manner as in Referential Example 1.Table 5 shows the results. This film had a high photoelastic constant of42×10⁻¹² Pa⁻¹ and had large birefringence caused by stress. Further, itschromatic dispersion does not meet λ/4 in a short wavelength region, andthere is caused a problem of a color omission, etc.

Comparative Example 7

<Production of Copolycarbonate>

A copolycarbonate was obtained in the same manner as in ComparativeExample 6 except that 639 parts of BPA and 1,881 of BCF were used.

<Production of Optical Film>

Then, a film was formed in the same manner as in Comparative Example 6,and measured for a photoelastic constant and a viscosity averagemolecular weight. Further, a sample that was taken in the same manner asin Referential Example 1 was monoaxially stretched 2.0 times at Tg+10°C. in the same manner as in Referential Example 1, and the thus-obtainedstretched film was measured for a retardation and chromatic dispersion.Table 5 shows the results. This film had a high photoelastic constant of45×10⁻¹² Pa⁻¹ and had large birefringence caused by stress. When it isused as a retardation film, therefore, a light omission undesirablytakes place. Further, its chromatic dispersion does not meet λ/4 in along wavelength region, and there is caused a problem of a coloromission, etc.

TABLE 4 Viscosity average molecular Photoelastic Monomer weight Tgconstant R(550) R(400)/ R(700)/ — — ° C. 10⁻¹² Pa⁻¹ nm R(550) R(550)Referential CHDM 18600  41 48 252 1.02 0.99 Example 1 Referential TCDDM18300  78 4 191 1.04 0.97 Example 2 Referential DOG 19100  53 13 1821.03 0.98 Example 3 Referential BPA 16800 148 80 481 1.23 0.94 Example 4Referential BCF 19300 244 30 −241 1.39 0.91 Example 5 Referential BPEF18800 153 35 −112 1.55 0.83 Example 6

TABLE 5 Viscosity average Compositional molecular Photoelastic Monomerratio weight Tg constant R(550) Negative Positive Negative Positive — °C. 10⁻¹² Pa⁻¹ nm

n Example 12 BCF CHDM 34 66 19200 116 39 148 0.0039 Example 13 BCF TCDDM34 66 19000 128 14 138 0.0039 Example 14 BPEF TCDDM 50 50 18800 115 20131 0.0036 Example 15 BCF DOG 34 66 18900 118 18 139 0.0043 ComparativeBCF BPA 67 33 36400 225 42 141 0.0020 Example 5  Comparative BCF BPA 6436 35900 220 45 148 0.0026 Example 6  R(400)/R(550) R(450)/R(550)R(650)/R(550) R(700)/R(550) Example 12 0.75 0.88 1.05 1.07 Example 130.72 0.85 1.04 1.06 Example 14 0.75 0.88 1.05 1.07 Example 15 0.75 0.891.05 1.07 Comparative 0.55 0.73 1.07 1.07 Example 4  Comparative 0.730.87 1.01 1.01 Example 5  |R(400)/R(550)-400/550|² + Contrast|R(400)/R(550)-400/550| |R(700)/R(550)-700/550| |R(700)/R(550)-700/550|²evaluation Example 12 0.02 0.20 0.0404 ◯ Example 13 0.01 0.21 0.0442 ◯Example 14 0.02 0.20 0.0404 ◯ Example 15 0.02 0.20 0.0404 ◯ Comparative0.18 0.20 0.0724 X Example 4  Comparative 0    0.26 0.0676 Δ Example 5 

EFFECT OF THE INVENTION

The retardation film of this invention is composed of a copolycarbonatehaving desired chromatic dispersion and a low photoelastic constant andhaving high-degree transparency and excellent processability, and it hasdesired chromatic dispersion owing to its stretching treatment and hascapability of performing in a broad band in the form of a single layer,so that it is remarkably useful as a retardation film for a liquidcrystal display and an organic EL display.

INDUSTRIAL UTILITY

The optical film of this invention is suitably used in an optical pickupfor use in a liquid crystal display and a recording device, an opticaldevice in an optical recording medium, a light emission device, anoptical operation device, an optical communication device and a touchpanel.

1. An optical film which comprises a copolycarbonate comprising 25 mol %or more but less than 65 mol % of a unit (A4) represented by thefollowing formula,

and over 35 mol % but 75 mol % or less of a unit (B1) represented by thefollowing formula,

wherein the optical film satisfies the following formulas (2) and (3),0<R(450)/R(550)<1  (2)1.01<R(650)/R(550)<2  (3) wherein R(450), R(550) and R(650) are filmin-plane retardation values at wavelengths of 450 nm, 550 nm and 650 nm,respectively.
 2. The optical film of claim 1, which satisfies thefollowing formulas (8) to (10),|R(400)/R(550)−400/550|<0.15  (8)|R(700)/R(550)−700/550|<0.25  (9)|R(400)/R(550)−400/550|² +|R(700)/R(550)−700/550|²<0.05  (10) whereinR(400), R(550) and R(700) are film in-plane retardation values atwavelengths of 400 nm, 550 nm and 700 nm, respectively.
 3. The opticalfilm of claim 1, which has a retardation exhibition capability (Δn)satisfying the following formula,0.3>Δn>0.002 (Δn=R(550)(nm)/thickness (nm)) wherein R(550) is a filmin-plane retardation value at a wavelength of 550 nm.
 4. A retardationfilm comprising the optical film of claim
 1. 5. A liquid crystal displaycomprising the retardation film of claim 4.